For mobile communications antennae, one-column or multi-column antenna arrays are generally used, and conventionally comprise in each column a plurality of radiators or radiator devices arranged above one another in the vertical direction. In this context, dipole radiators, such as are known from WO 00/39894 A1 or WO 2004/100315 A1, may be used, for example in the form of dipole crosses, dipole squares or what are known as vector dipoles. However other radiators and radiator shapes, for example patch radiators, are also possible.
The antenna arrangement may be a single-band, a dual-band, or preferably a multi-band antenna arrangement which preferably transmits and receives in two mutually perpendicular polarisation planes, rather than just in one polarisation plane. These polarisation planes are preferably aligned in the manner of what is known as an X polarisation, meaning that the two mutually perpendicular polarisation planes are aligned at a +45° and a −45° angle to the horizontal (or vertical).
A dual-polarised group antenna of this type according to the prior art should conventionally be able to generate two radiated field patterns which correspond or can be correspondingly controlled, namely a radiated field pattern for each of the two linear polarisations i.e. for both of the mutually perpendicular polarisation planes. These should be electrically independent of one another. Thus, on the one hand the cross polarisation distance of the radiation must be very large. On the other hand, the coupling between the antenna terminals should be very low, i.e. the decoupling (isolation) should be very high.
This is true for every frequency band as a matter of basic principle. Thus, all specifications should be met for the entire frequency range (frequency band). This also applies in the case of a dual-band or even multi-band group antenna, since more and more frequency ranges are currently being allocated to mobile communications. Meanwhile, a mobile communications antenna should cover a frequency range of for example 1710 MHz to 2690 MHz. This corresponds to a bandwidth of 980 MHz or a relative bandwidth of 45% based on the mean frequency. This makes it more difficult and demanding to meet all of the requirements over such a large frequency range. A further complicating factor is that a second, disjoint frequency band of for example 806 MHz to 960 MHz may also be set, and that some of the radiators and radiator devices are then formed or must then be formed as dual-band radiators, as explained above. This increases the total number of radiators and radiator elements between which interactions can take place.
Lastly, a group antenna may also further comprise a plurality of adjacent columns, in such a way that for radiators which are arranged in two different antenna columns, not only the decoupling between two mutually perpendicular polarisation planes in relation to the radiators or radiator devices of an antenna column, but also the decoupling between identical polarisations must be taken into account.
Against this background, there is a need for a group antenna in particular with better decoupling between the two polarisations. This applies for example both to a single-column dual-polarised antenna and to a multi-column antenna.
Thus, WO 00/31824 A1 has already proposed a group antenna which comprises spatially separated groups of single-polarised radiators for each polarisation. However, this results in an extremely high space requirement, in such a way that in practice, systems of this type cannot be implemented.
WO 2004/051796 A1 proposes a two-dimensional array of group antennae, a respective radiator arrangement being provided in each of the at least two vertically extending columns and these arrangements being powered separately from one another. In this case, at least one radiator or radiator device is provided for example in the second column and is powered together with the radiators or radiator arrangements in the first antenna column. Conversely, at least one radiator or radiator device is provided in the first antenna column and is powered together with the radiators in the second antenna column. Ultimately, this does serve the beam-forming process, but not in such a way as to allow an improvement in the decoupling to be achieved.
WO 2008/060206 A1 also proposes an antenna array with dual-polarised radiators, which in each case comprise at the edges a region with single-polarised radiators with the same polarisation. In this case, the number of radiators which are interconnected in a group varies. This too should produce a different radiated field pattern. In other embodiments, a two-column antenna is proposed, in which for example in one column, radiators are aligned only in one polarisation direction, and in the second column, the radiators are aligned only in a polarisation plane perpendicular thereto, the distance between the radiators with the same polarisation plane being different in the two antenna columns. As stated, these measures all serve to produce different radiated field patterns.
Against this background, the present invention is based on prior art which is basically shown in FIG. 10.
For this purpose, a category-defining antenna array according to FIG. 10 comprises for example a plurality of radiator devices 3, which are formed as dual-polarised radiator devices and for this purpose comprise radiators or radiator elements 3a which are powered, and thus transmit and/or receive, in a first polarisation plane and second radiators or radiator elements 3b which receive and/or radiate, in a second polarisation plane P2 perpendicular to the first polarisation plane P1. Preferably, the two polarisation planes are at a plane angle of ±45° to the vertical or horizontal.
The aforementioned radiator devices shown in FIG. 10 are thus arranged adjacent to one another in the installation direction 5 (a linear arrangement), above one another in the embodiment shown. In this respect, it is also possible to speak of a single-column group antenna, i.e. a group antenna with an antenna column 7, which is conventionally aligned in the vertical direction or predominantly in the vertical direction, but may in principle also be aligned in the horizontal direction and in any other desired direction with a vertical and a horizontal component. For simplicity, in this respect the following will always refer to an antenna column independently of the alignment thereof.
The aforementioned radiator devices 3 are thus conventionally arranged in front of a reflector 1. The dual-polarised radiators may for example be radiator devices in the form of a dipole, for example dipole crosses, dipole squares, vector dipoles etc., such as are known from the aforementioned document WO 00/39894 A1. Patch radiators and other radiators devices are also possible. There are no limitations in this respect.
The radiators 3a for one polarisation plane P1 are powered via a network N1, whereas the radiators 3b which transmit in the second polarisation plane P2 are powered via the network N2.
Based on the prior art, the object of the present invention is now to provide an improved antenna array, which can in principle be single-column or multi-column, and which can be operated in one band or preferably also in a plurality of bands, it being possible by simple means to achieve better decoupling between the polarisations of dual-polarised radiators in one column and/or better decoupling for radiator devices with the same polarisation plane in adjacent columns.
The object is achieved according to the invention by the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.
The solution according to the invention is distinguished in that a dual-polarised group antenna comprises three different regions or three different types of radiator arrangement or ways of powering the radiator arrangements, it being provided that at least one and preferably a plurality of radiator devices are powered in both of the mutually perpendicular polarisation planes, and in that each antenna column is allocated at least one further additional radiator device, which is powered either only in the first polarisation plane or only in the second polarisation plane. The additional radiator arrangements may be single-polarised radiators or alternatively dual-polarised radiators, which unlike the other radiators are powered only in one polarisation plane.
In this case, the total number of radiators in group antenna which are powered with the first and the second polarisation is equal.
Conventionally, dual-polarised antennae are constructed to be as similar as possible, to obtain similar radiated field patterns in both polarisation planes. Thus, the best decoupling would also be expected with a symmetrical construction. This makes it all the more surprising that the invention achieves an improvement by means of an asymmetrical configuration of the antenna array, since in the context of the invention the arrangement of the radiators and/or the operation of the radiators are no longer necessarily similar or symmetric. This is because the configurations and/or positions are different for the active radiators or radiator devices in the groups of radiator devices allocated to both polarisations. The two polarisations of a dual-polarised radiator are used in parallel in part (as was also previously the case), whereas now, according to the invention, other further single- or dual-polarised radiators spatially separated from one another are provided, but in the case of the dual-polarised radiator are only operated in one polarisation plane. This construction, which is slightly more complex in itself, nevertheless ultimately leads to a partial spatial separation of the two polarisation planes, and thus surprisingly contributes to the improved decoupling. The improvement in the decoupling in this case may be so great that the entirety of all the other specifications or radiation diagrams, adjustments and the desired bandwidth requirements can be met.
Two dual-polarised antennae with similar or identical frequency ranges can also be arranged behind one another along a single column. In the context of the present invention, a dual-polarised radiator can be used in the centre for example of the of the +45° polarisation of the first antenna and simultaneously of the −45° polarisation of the second antenna. Single-polarised radiator devices, which radiate either in one polarisation plane or in the other polarisation plane, can be arranged above and below.
If two antenna columns are arranged adjacent to one another, then there can be additional dual-polarised radiators, of which one polarisation plane is allocated to one column and the other polarisation plane is allocated to the second antenna column, i.e. to the radiators or radiator devices powered in one or other antenna column respectively.